1. Field of the Invention
This invention relates to an antijamming safety device adapted for use in a paper feeding mechanism in a copying machine, and particularly to a device for preventing troubles that might result from jamming of copying sheet materials after detecting such jamming. More specifically, the present invention is envisaged to provide an antijamming safety device of the type described, whereby when jamming of copying sheet materials is detected, only those means or elements which can bring about a dangerous condition unless they are promptly disconnected from power when said jamming occurs, such as for example heating means, are immediately disconnected from power. Then, after a delay period, jam indicating means are activated to let the operator know of such jamming, so that appropriate safety measures can be taken.
2. Description of the Prior Art
In copying machines or such, it is often experienced that the copying sheet materials such as sensitive paper, transfer paper, etc., may become held up in their passage through the machine (such phenomenon being hereinafter referred to as jamming). It is next to impossible with the existing techniques to perfectly exclude such jamming in copying machines. Therefore, efforts have been exerted for developing a method or a mechanism for detecting such jamming of sheets. In most systems, jamming of sheets is detected by a sensing device and the fixing heater or driving motor is immediately shut down by the output thereof, or a jam indicator lamp is lighted to let the operator know of such jamming, thereby to prevent trouble or breakdown that could result from such jamming.
However, if all the working means are shut down immediately after detection of jamming, a dangerous condition could rather be created. That is, in a copying machine, if delivery of certain copying sheets is slightly delayed after the specified setting, such delay can be sensed as jamming. In such a case, if an indication of jamming is given, the operator will immediately turn off the power switch, some copying sheets are still in the fixing unit. There is therefore a danger that such copying sheets may catch fire due to the thermal inertia of the heater in the fixing unit.